Nowadays, a demand for power generation using renewable energy increases, and particularly solar power generation or solar thermal power generation using sunlight attracts attention.
For example, a solar power generation facility ranges from a facility having a power generation capacity of about 3 kilowatts to about 4 kilowatts provided in a standard home to a commercial large-scale power generation facility having a power generation capacity exceeding 1 megawatt. Even in the solar thermal power generation facility, there are many large-scale facilities having the power generation capacity exceeding 1 megawatt, and the solar thermal power generation facility is also expected as the alternative power generation facility for thermal power generation or nuclear power generation.
The power is generated by receiving solar radiation light from the sun in power generation such as the solar power generation and the solar thermal power generation, in which sunlight is used. Therefore, when a light receiving surface of the solar cell array (that is, a solar cell module) or the condensing mirror gets dirty, in the solar power generation, light transmission of a cover glass constituting the light receiving surface of the solar cell module degrades according to a level of dirt to decrease a power generation amount. In the solar thermal power generation, a reflection rate of the condensing mirror degrades to decrease the power generation amount. That is, in the solar power generation or solar thermal power generation, when the light receiving surface of the solar cell module or condensing mirror gets dirty, power generation performance degrades largely.
Therefore, it is necessary to properly clean the solar cell array and the like to remove dirt on the light receiving surface of the solar cell array and the like.
The facility provided in a standard home can periodically be cleaned by a person. On the other hand, because the large-scale solar power generation facility has a huge surface area, it is difficult for a person to clean to remove dirt on the surface of the solar cell array. For example, it is assumed that a 1-megawatt solar power generation facility is constructed with solar cell modules each of which has power generation output of 100 watts. In this case, 10000 solar cell modules are provided in the whole solar power generation facility. In the case that one solar cell module has a 1-square-meter area, the area to be cleaned becomes 10000 square meters. Plural solar cell arrays each of which has a set of plural solar cell modules are provided in the solar power generation facility, the area of solar cell array ranges from about 50 square meters to about 1000 square meters although it depends on various field conditions. Accordingly, the self-propelled robot that can run on the surface of the solar cell array and the like in an automatic or remote control manner becomes efficient cleaning unit in the large-scale solar power generation facility.
Nowadays various autonomous-travel cleaning robots are developed in order to automatically clean a building floor and the like (for example, see Patent Document 1), and it is conceivable that these autonomous-travel cleaning robots are used as the robot that cleans the solar cell array and the like.